Tach Puzzle

The hood tack on my '69 GTO works great for about 10 minutes and then stops registering anything once the engine warms up. Connections appear to be solid. Any ideas as to why this could be happening?

If your connections are good then check the routing of your harness it might to close to a heat source seeing that it wants to stop working after the car heats up good luck with your problem.

Make sure the connection is directly on the negative terminal of the distributor, and not the wire the leads from it. If you used the lead otu wire, it may be connected to the choke, and once the engine is warm, you'll loose the ground.